A feedback-mode variant of thermal lens spectrometry was employed for steady-state photothermal measurements and time-resolved studies of thermal lens formation dynamics to compare the precision and sensitivity of measurements in aqueous polyethylene glycol (PEG) solutions of different molecular weights using a series of model systems (ferroin, cobalt complexes with nitrosonaphthols, and aqueous fullerene dispersions). The results of thermal lens measurements obtained in single-phase aqueous PEG solutions were compared with those obtained under extractive preconcentration conditions in PEG-based aqueous two-phase systems. Time-resolved thermal lens development curves in PEG-containing media were shown to exhibit greater stability and improved temporal separation between the thermal lens effect itself and the interfering thermophoresis phenomenon (the Soret effect) than those recorded in polymer-free aqueous media. To improve the accuracy of thermal diffusivity measurements, experimental conditions were selected under which the deviation from the theoretical curve development was minimal, and the Soret effect was absent (50–300 ms from the beginning of the measurement cycle). In PEG-containing media, the dynamics of thermal lens development showed better agreement with theory even for finely dispersed systems (aqueous fullerene dispersions), resulting in a substantial increase in the sensitivity of thermal lens measurements. The precision of thermal lens measurements in PEG solutions was higher than that in aqueous solutions because of lower signal fluctuations, which further enhanced the sensitivity of thermal lens measurements in such media. Conditions were proposed for the extraction-thermal lens determination of cobalt with 2-nitroso-1-naphthol based on the partitioning of the colored complex in an aqueous two-phase system composed of PEG and phosphate ions (K2HPO4, NaH2PO4, or NH4H2PO4), followed by thermal lens determination in the extract phase. The detection limit for cobalt with 2-nitroso-1-naphthol in the phosphate–PEG aqueous system was 1 μmol/L (532 nm, excitation laser power 10 mW), whereas the detection limit for cobalt with nitroso-R salt in the ammonium sulfate–PEG aqueous system (excitation laser power 100 mW) was 0.2 μmol/L. For aqueous fullerene dispersions, a twofold increase in measurement sensitivity was demonstrated compared with aqueous media without PEG.
Creatinine is a key marker for renal function, and accurate measurement of creatinine in serum is important for clinical diagnostics. In the present work, a new colorimetric method using the creatinine-chlorophenol red (CPR) reaction was introduced and conducted with ultraviolet-visible and paper-based microfluidic (µPAD) measurement. Optimal conditions were established for each method, whereas analytical performance in terms of linearity, sensitivity, precision, recovery, and comparison with the reference analyzer (Cobas c311) was evaluated. A spectrophotometric method based on the formation of a pink-violet ion-pair complex and its bathochromic shift with an absorption maximum at 576 nm was developed, linear over 2–130 µg/mL, the limit of detection (LOD) was 1.2 µg/mL, and the limit of quantification (LOQ) was 2.25 µg/mL. Finally, the µPAD-based assay was optimized using a higher CPR concentration (100 µg/mL) and had a linear range of 10–160 µg/mL (R2 = 0.9972), and LOD and LOQ were 7.0 and 11.57 µg/mL, respectively. Recovery values between 97.1 and 104.3
A version of competitive fluorescence polarization immunoassay (FPIA) and an amperometric immunosensor with a tyrosinase tracer have been developed for the sensitive and selective determination of the chloramphenicol antibiotic. In the development of FPIA for the determination of chloramphenicol, a green fluorescent complex of terbium(III) was first used as a tracer, which changed emission in the green spectral region with a maximum at 545 nm. The competitive binding of the substance to be determined with a limited number of binding sites of specific antibodies (ABs) in using this tracer ensured the determination of chloramphenicol in the linear range of the calibration dependence of fluorescence polarization on the analyte concentration in the range 1 × 10–11–1 × 10–7 M, LOD = 9 × 10–12 M. To ensure the maximum value of the analytical signal, tracer dilution was selected at 1 : 10 and antibody dilution, at 1 : 25. The optimal incubation time for the tracer–antibody immune complex was 5 min. Tyrosinase enzyme was used as a tracer in the development of an amperometric enzyme-linked immunosorbent assay (ELISA) sensor for the detection of chloramphenicol. The work of this sensor is based on a combination of immunochemical, enzymatic, and electrochemical reactions, leading to “quasi-inhibition” effects. The developed amperometric immunosensor for the determination of chloramphenicol ensured its determination in a narrower concentration range from 1 × 10–9 to 1 × 10–6 M, LOD = 8 × 10–10 M. The conditions of analysis were as follows: AB dilution of 1 : 200 and the duration of an analysis 10 min. The developed versions for the determination of chloramphenicol were tested in analyses of food products (milk). The error of the determination dis not exceed 0.059.
This paper presents the results of original research on nondestructive quality control of food products and solid dosage forms of pharmaceuticals using digital colorimetry with a smartphone and chemometric processing of the resulting spectral data.
Silica monolithic rods are inorganic materials used as packing materials in monolithic separation columns, a global trend in material separation, particularly in high-performance liquid chromatography (HPLC). Unlike the previously widely used separation columns with spherical silica packing, these monolithic columns suffer from various problems, including shrinkage, deformation, and cracking during the preparation of rods, limiting their application. This paper describes the development of a new type of silica monolithic rod that can significantly shorten analysis time while maintaining high separation efficiency in HPLC.
This study presents the first application of an analytical quality by design approach using face-centered central composite design to optimize an ultraviolet-visible spectrophotometric method for the estimation of amphotericin B (Amp B). The optimal critical method parameters established using the desirability approach indicated a detection wavelength of 385 nm in a solvent of 0.1 N HCl (pH 1.2), which significantly improved (p < 0.05) the extinction coefficient while minimizing aggregation. The method, when validated as per ICH Q2(R2), displayed high linearity (R2 = 0.997) in the concentration range from 6–36 µg/mL. The method was found to display high accuracy, with recoveries ranging from 95.41 ± 0.02
The article presents solutions corresponding to protocols for the formation of structured clusters of DNA fragments in filling a flow cell for the high-throughput DNA sequencing taking into account various integral quality indicators. Conditions for implementing a possibility of the detection of a polyclonal cluster were investigated. Recommendations are given for choosing an algorithm of cluster formation depending on the relative importance of the following characteristics: minimization of the number of microwells, minimization of the fraction of “lost” DNA fragments and/or used microwells, maximization of the speed of analysis, and various combinations of the specified requirements.
The adulteration of citronella (Cymbopogon winterianus) oil with a cheaper alternative, such as low-grade turpentine oil, is a recurring issue in the essential oil industry, posing risks to product quality and consumer safety. A rapid and non-destructive authentication method is therefore essential for quality control of this product. This study utilized Fourier-transform infrared spectroscopy followed by principal component analysis (PCA) and partial least squares (PLS) regression for qualitative and quantitative authentication of citronella oil mixed with turpentine oil, respectively. Samples were prepared with various adulteration concentrations of citronella oil in turpentine oil (0 to 100
A sensitive approach to the determination of trace amounts of phosphate ions in aqueous solutions using surface-enhanced Raman spectroscopy on silver nanofilms modified with cetyltrimethylammonium bromide was proposed. The role of a surface modifier in enhancing the analytical signal was investigated. For pure sodium hydrogen phosphate solutions, the detection limit was 60 nM (5.7 μg/L), and the calibration function was linear over the hydrogen phosphate ion concentration range of 1 × 10–7 to 1 × 10–4 M.
A procedure for determining doxorubicin in the presence of bortezomib in model aqueous solutions and blood plasma is developed based on the fluorescence quenching of CdZnSeS/ZnS and AgInS/ZnS quantum dots. Since doxorubicin is often used in combination chemotherapy with bortezomib, monitoring its plasma concentration is important for increasing the effectiveness of chemotherapy and reducing the risk of side effects. The sensitivity of doxorubicin determination in the presence of bortezomib (0.3 μM) is compared using quantum dots with different surface ligands. A trend toward decreased fluorescence quenching efficiency of quantum dots by doxorubicin in the presence of bortezomib is demonstrated. The use of alloyed CdZnSeS/ZnS quantum dots stabilized with 3-mercaptropropionic acid for the determination of doxorubicin in the presence of bortezomib in plasma is demonstrated, with a detection limit of 0.08 μM and a quantification limit of 0.24 μM.
The article is devoted to the use of multichannel microgravimetry for assessing the functional properties of organic phosphors of the azolotriazine class as promising analytical reagents for test systems for liquid and gas media. The promise of using azolotriazines of various structures as analytical reagents in test systems for liquid and gas media is estimated. The primary objectives of the study were to identify the most stable and selective structures of the synthesized organic compounds based on heterocyclic ring systems of imidazo-, pyrazolo-, and triazolotriazines; to assess their properties and potential use as analytical reagents for volatile organic and some inorganic (water, ammonia) compounds (VCs) for use in portable test systems. The study covered two fields: the assessment of changes in the optical properties of the reagents in various media (solutions, solid substrates) for visual test systems, and an analysis of the kinetics of sorption of VC vapors by piezoelectric quartz resonators (FLU-1 array) modified with fluorimetric reagents in the injection and frontal sample introduction modes in combination with highly sensitive microgravimetry. Compounds of the highest stability in solution and on a solid support (4-(6-oxo-2-phenylimidazo[1,2-b]pyrido[4,3-e][1,2,4]triazin-7(6H)-yl)butanoic acid (I), 3-hydroxy-2-(6-oxo-2-phenylimidazo[1,2-b]pyrido[4,3-e][1,2,4]triazin-7(6H)-yl)propanoic acid, 3-methyl-6-phenylimidazo[1,2-b][1,2,4]triazine-2-carbohydrazide) were identified, as well as those demonstrating selectivity to the key analytes formed during food spoilage, i.e., butyric acid, propionic aldehyde, cyclohexanone, and aromatic amines. The results indicate that azolotriazines ensure the differential recognition of complex VC mixtures, including real samples, by interpreting paired sensitivity spectra A(i/j) and kinetic “visual fingerprints” of the signals of sensor with the selected best phases. A chemometric RGB space method with integral color labels of the results of vapor detection by piezoelectric quartz microbalances with new sorbents confirmed the applicability of compounds I and 7-(2-aminophenyl)pyrazolo[5,1-c]pyrido[4,3-e][1,2,4]triazin-6(7H)-one to the identification of water, ethanol, and organic acids. However, to ensure the accuracy of an analysis, it is important to completely remove residual polar solvents (DMSO) affecting phase selectivity. A protocol was proposed for the rapid screening of luminophore, with the assessment of visual brightness, stability, and gravimetric vapor weighing efficiency under both batch and dynamic conditions. This step confirmed the feasibility of integrating individual azolotriazines into sensor platforms for monitoring the quality of food and biomedical systems and indicated a direction for optimizing the structures of potential reagents by adjusting donor–acceptor properties of the substituents in the luminophore molecule and minimizing artifacts associated with the residual synthesis components and the nature of the substrates. The data obtained provide a basis for the development of portable analytical facilities with multimodal response, overcoming the limitations of the traditional fluorescence systems, such as reduced selectivity in multicomponent media and instability under operation conditions.
Studying the structure and mechanisms of photoluminescence (PL) formation in carbon nanoparticles, particularly carbon dots (CDs), is a topical issue in various fields of nanosensors. A key step in solving this problem is obtaining a homogeneous solution of the synthesized nanoparticles. In this study, two types of CDs with different ratios of ethylenediamine (EDA) and citric acid (CA) precursors are synthesized using a hydrothermal method. The synthesized CDs are separated into fractions using gel electrophoresis. It is found that the photoluminescence, optical density, and PL lifetime of the isolated CD fractions synthesized from EDA and CA depend significantly on the pH of the water. A theory is put forward that changes in the spectral characteristics of CD fractions with pH are due to the protonation/deprotonation of imidazole amino groups in the luminophores of these fractions.
An important issue to consider when determining the chemical composition of slag wool (CCSW) is sample digestion due to the complexity of the matrix. Some methods usually employed to determine the composition of silicate rocks and minerals have been adapted to determine CCSW. However, the dissolution characteristics between rock/glass and slag wool fibers are rather different and thus affect quantitative analysis. The present work reports a reliable, quantitative, low-cost method for the determination of CCSW based on sample fusion, acid dissolution, and subsequent analysis by flame atomic absorption spectrometry. Some oxides were analyzed by gravimetry, allowing the overall chemical characterization of slag wool. Scanning electron microscopy/energy dispersive X-ray spectrometry and traditional current methods were performed for comparison. A study regarding the effects of sample amount and particle size is presented. The results show that the proposed method allows determining CCSW with accuracy; in addition, it offers the advantage of reducing both the melting temperature and the sample preparation time, representing a lower-cost analytical method for the determination of CCSW.
The possibility of colorimetric determination of catecholamines using silica nanodots with a digital camera and smartphone is demonstrated. A lamp and a diode with emission wavelengths of 395 and 360 nm, respectively, are used as excitation sources. Color coordinates in the RGB, CMYK, and Lab systems, as well as some combinations thereof, are used as analytical signals. It is demonstrated that using a lamp as a source of ultraviolet radiation allows for achieving the best detection limits for all three catecholamines: 7, 0.1, and 1 μM when using a camera, and 12, 0.3, and 5 μM for dopamine, norepinephrine, and epinephrine, respectively, when using a smartphone. The data are obtained for the Euclidean distance analytical signal in the CMYK system. Using a camera and other color coordinate combinations as analytical signals can reduce the detection limits to 0.1 μM for epinephrine (coordinate combination L-a + b) and to 1 μM for dopamine (coordinate combination R + G + B). The pharmaceuticals “Dopamine-Ferein” (ZAO “Bryntsalov-A,” Russia), “Adrenaline Hydrochloride—Vial” (VIAL, China), and “Noradrenaline” (ZAO “EcoPharmPlus,” Russia) are analyzed. The results of colorimetric determination are in good agreement with the luminescence and HPLC analysis data.
Infant formula is an alternative to breast milk for newborns when breastfeeding is not possible for any reason. This study examines vibrational spectroscopic methods, namely near-infrared spectroscopy (NIR) and attenuated total reflectance infrared spectroscopy (ATR-IR) in the mid-infrared region, for the determination of phospholipids in infant nutrition products. Chemometric methods were applied for processing the spectroscopic data, including principal component analysis (PCA) and partial least squares regression (PLS). PCA demonstrated clustering of samples into groups according to their phospholipid content. Using PLS models based on ATR-IR and NIR spectra, it is possible to determine major classes of phospholipids with sufficient accuracy, including phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin, as well as total phosphorus content (coefficients of determination R2 greater than 0.94 and 0.96 for ATR-IR and NIR data, respectively; mean squared prediction error less than 0.14
The work is devoted to the development of a method for the sorption–fluorometric determination of enrofloxacin in aqueous solutions using sensitized fluorescence on the surface of a nanofiber formed by electrospinning. Enrofloxacin is a broad-spectrum antibacterial agent; as an inhibitor of bacterial DNA gyrase, it is widely used in livestock, poultry, and fisheries, and as a growth promoter and in food additives. However, the wide and often unjustified use of antibacterial substances is a reason for exceeding the permissible values of their residual quantities in the food raw materials and food products and in natural and waste waters, which necessitates monitoring of their contents. The effect of the nature of polymer fibers, the concentration of terbium ions, the acidity of the medium, and the nature of the surfactant on the recovery of enrofloxacin and the fluorescence intensity of the analytical system was studied. Polyacrylonitrile fiber formed from a 13
Raman spectroscopy (RS) in combination with machine learning methods was used to solve the problem of the classification of adipose tissue before and after exposure to lipase. Differences between the classes were identified using principal component analysis. Hyperparameters such as the number of trees (n_estimators) and the maximum depth (max_depth) of the random forest (RF) and gradient boosting (GB) ensemble models are optimized for balanced accuracy and training time. This made ensured obtaining models with high predictive ability. In this method, models with 50 decision trees with a maximum depth of 3 were trained. The weighted accuracies of the RF and GB models were 96.4 ± 8.7
A novel arsenic-free method for the determination of iodine in urine was developed using a cerium(IV)−Ferroin catalytic reaction combined with an automated biochemistry analyzer. The method was based on the oxidation of the Ferroin reagent by cerium(IV) ions in an acidic medium, followed by reduction with hydrazine hydrochloride. Iodide ions catalyzed the reaction, and the absorbance was measured using an automated biochemistry analyzer. A quadratic relationship between iodine concentration (c, μg/L) and absorbance (A) was observed within the range of 0–400 μg/L and was described by the regression equation c = aA2 + bA + d, with a coefficient of correleation (r) greater than 0.999. The method exhibited high sensitivity, with a limit of detection for urinary iodine of 3.6 μg/L. Excellent precision was achieved, with an intra-assay coefficient of variation (CV) of ≤3.0
An analysis of the data published in the last decade on the use of magnetic nanoparticles (MNPs) modified with inorganic, organic, and polymeric substances for the sorption and preconcentration of anionic azo compounds used as indicators, organic reagents, food and textile dyes in water media and also in food and environmental samples is presented. The main focus is on the revelation of the effect of the modifier nature and sorption conditions (pH; dye concentration; MNP weight, specific surface area, pore diameter, and volume; zeta potential; and magnetization value) on the recovery, sorption and desorption time, and also on the sorption capacity of the MNPs with respect to various acidic mono- and bisazo dyes. The main trends in the development of methods of magnetic solid-phase extraction are noted.
Conditions are selected for the separation of artificial sweeteners on sorbents based on silica and poly(styrene–divinylbenzene) in the hydrophilic interaction liquid chromatography conditions using a diode array and an evaporative light scattering detector. The mechanism of the retention of sugar substitutes on sorbents based on poly(styrene–divinylbenzene) is revealed. The separation of aspartame, acesulfame, and saccharin and their determination in diet drinks on mixed-mode stationary phases was performed for the first time. The limits of detection are 8 μg/mL for aspartame, 0.6 μg/mL for acesulfame, and 1 μg/mL for saccharin at an analysis time of 17 min. The applicability of the resulting sorbent and the method for determining sugar substitutes to the analysis of beverages was assessed.
